The present invention relates to a coil for an electric rotary machine and its manufacturing method, and more particularly to a stator of an automotive electric rotary machine equipped with a coil consisting of serially joined conductor segments and its manufacturing method. Furthermore, the present invention relates to a method for manufacturing an electric rotary machine using this coil.
A conventionally proposed stator coil consists of numerous conductor segments which are inserted into slots of a stator and serially joined each other. For example, Japanese patent No. 3118837 (corresponding to U.S. Pat. No. 6,249,956) or Japanese patent No. 3196738 (corresponding to U.S. patent application publication No. 2002/0053126), owned by the same applicant as that of this application, discloses a method for manufacturing this type of coil according to which U-shaped conductor segments are serially joined.
According to this kind of segmental serial-joint type stator coil, a pair of legs of a conductor segment are separately inserted into different slots of a rotor spaced by an angle equivalent to a pole pitch. A protruding part of each leg is bent in the circumferential direction. Then, the distal ends of the legs of different conductor segments are successively joined.
More specifically, the conductor segment consists of a U-shaped (more accurately, a V-shaped) head conductor portion, a pair of in-slot conductor portions extending from both ends of the head conductor portion and inserted into different slots from one axial side of a core, and a pair of tail conductor portions protruding out of the slots from the other axial side of the core and extending in the circumferential directions. The distal ends of the tail conductor portions of different conductor segments are joined together. Hereinafter, the in-slot conductor portion and the tail conductor portion may be collectively referred to as a leg of the conductor segment. Accordingly, the head conductor portions of respective conductor segments cooperatively constitute a first coil end (i.e., a head side coil end). The tail conductor portions of respective conductor segments cooperatively constitute a second coil end (i.e., a tail side coil end).
Hereinafter, a conventional method for manufacturing this kind of segmental serial-joint type stator coil disclosed in the above-described prior art documents will be explained.
First, a required number of pine-needle conductor segments are prepared. Each prepared pine-needle conductor segment has two elongated legs neighboring to each other and extending straight from its head.
Next, each pine-needle conductor segment is configured into a U-shaped conductor segment with a pair of in-slot conductor portions angularly spaced by one pole pitch in the circumferential direction. Then, the U-shaped conductor segments are spatially disposed (more specifically, aligned in the circumferential direction) so that a required number of conductor segments are simultaneously inserted into each slot of the stator core. For the above-described process, it is possible to use a pair of coaxial rings having insertion holes, for example, disclosed in FIG. 3 of Japanese Patent No. 3118837. According to the manufacturing process shown in this prior art, both legs of a pine-needle conductor segment are inserted into two adjacent holes of the coaxial rings which are positioned in the same angular position. Then, the coaxial rings are mutually rotated about their axes by the amount corresponding to one pole pitch in the circumferential direction. As a result, each pine-needle conductor segment is configured into a U-shaped conductor segment with a head portion straddling so as to form, as a whole, a U shape in the circumferential direction.
Next, a process for inserting each conductor segment, formed into a U-shaped configuration and aligned in the circumferential direction, into a slot of the core is performed. This process is performed by pulling the legs out of the rings having insertion holes, while holding the head conductor portions of respective conductor segments each being formed into a U-shaped configuration and aligned in the circumferential direction, and then inserting the legs of respective conductor segments into slots of the core.
When a total of four in-slots conductor portions are aligned in the radial direction in the same slot, a small U-shaped turning conductor segment and a large U-shaped turning conductor segment are manufactured. Two legs of the small U-shaped turning conductor segment are simultaneously inserted into slots of the core according to the above-described method. Then, two legs of the large U-shaped turning conductor segment are simultaneously inserted into slots of the core according to the above-described method. However, it is of course possible to insert the U-shaped conductor segments into slots one by one. The process for configuring each pine-needle conductor segment into a U-shaped conductor segment can be performed by press work without using the above-described rings with insertion holes.
Next, a process for bending each tail conductor portion protruding out of the slot in the circumferential direction is performed. Preferably, each tail conductor portion is bent in the circumferential direction by a half pole pitch. Such circumferential bending process is performed by using a plurality of coaxial rings having insertion holes, for example, disclosed in FIGS. 4 and 5 of Japanese Patent No. 31967398. The distal ends of tail conductor portions are inserted into insertion holes of the coaxial rings. Then, each coaxial ring is rotated in the circumferential direction by a half pole pitch (electric angle of π/2), so that each tail conductor portion is bent in the circumferential direction by a half pole pitch. When each coaxial ring is rotated in the circumferential direction, it is preferable to urge the coaxial ring in the axial direction so as to advance toward the tail conductor portion. The curvature at the bend point can be enlarged.
Next, a process for welding the distal ends of the tail conductor portions is performed. According to the above-described example, the small U-shaped turning conductor segment and the large U-shaped turning conductor segment are accommodated in the same slot in such a manner that a total of four in-slot conductor portions are aligned in the radial direction. In this case, the in-slot conductor of the innermost layer and the in-slot conductor of the outermost layer are mutually connected via a head conductor portion of a large U-shaped turning conductor segment. The in-slot conductor of the inner middle layer and the in-slot conductor of the outer middle layer are mutually connected via a head conductor portion of a small U-shaped turning conductor segment. The distal end of a tail conductor portion of the innermost layer is welded to the distal end of a tail conductor portion of the inner middle layer. The distal end of a tail conductor portion of the outermost layer is welded to the distal end of a tail conductor portion of the outer middle layer. Through the above-described welding process, an endless phase coil, as a coil representing one of the phases, is formed. To form extraction terminals of each phase coil at the head side, one of U-shaped head conductor portions is cut at an appropriate position. When the extraction terminals are formed to be long enough, the elongated portions can be bent in the circumferential direction so as to provide a connecting wire for a neutral point. The reason why such extraction terminals are formed at the head side coil end is to avoid the interference with the welding process performed at the tail side coil end.
Preferably, on pole pitch is constituted by six neighboring slots. An electric angle of 2π is constituted by 12 neighboring slots. In this case, the slot layout is expressed by U, X,−V,−Z, W, Y,−U,−X, V, Z,−W, and −Y. According to this slot layout, the mutually neighboring U-phase and X-phase coils are serially connected with a neutral point at one end and a U-X output terminal at the other end. The mutually neighboring W-phase and Y-phase coils are serially connected with a neutral point at one end and a W-Y output terminal at the other end. The mutually neighboring V-phase and Z-phase coils are serially connected with a neutral point at one end and a V-Z output terminal at the other end.
However, according to the above-described segmental serial-joint type stator coil, the U-shaped head conductor portion of the U-shaped conductor segment is sharply bent at an opening of the slot through which the conductor segment is inserted. The U-shaped conductor segment inclines in the circumferential direction. Hence, an insulating resin film covering the surface of the conductor segment directly faces the sharp edge of the slot opening. When the conductor segment is subjected to any stress or damage, the insulating resin film of the conductor segment will be worn. The insulation properties will be worsened. In general, an insulating sheet intervenes between the core and the conductor segment so as to insulate the in-slot conductor portion from the inner surface of the slot. However, it is known that surface discharge occurs between neighboring conductor segments. Considering this fact, it is very important to improve electric insulation properties of the U-shaped head conductor portion of each conductor segment whose roots are bent at the slot opening.
Furthermore, the head side coil end is constituted by U-shaped head conductor portions which are bent in the circumferential direction at the portion very close to the slot opening. This arrangement significantly reduces a clearance for cooling air flowing in the radial direction. Especially, a circumferential cross-sectional area available for the cooling air is insufficient at a portion adjacent to the end surface of the core. Hence, the cooling ability of the core is worse.
Furthermore, the cooling ability of the coil is a decisive factor for an advanced electric rotary machine which is compact in size and large in output power. The cooling ability of the coil is greatly dependent on the coil ends because heat exchange between the coil and the cooling air is chiefly performed at the coil ends. The cooling surfaces of the coil end is roughly proportional to the longitudinal length of the coil end. Accordingly, to improve the cooling ability of the coil, it is necessary to increase the longitudinal length (i.e., extension length) of each U-shaped head conductor portion. However, this leads to undesirable increase in the axial length of the head side coil end and will result in a significant scale-up in the size as well as in the weight of a resulting rotary machine.